The present invention relates to rotary electrical devices such as synchros and angular position transducers of the type known variously as resolvers, rotary inductors, rotary variable differential transducers, angular shaft position encoders, and the like. It particularly concerns such a device employing a solid rotor, i.e., one which has no electrical windings thereon.
Using an angular position resolver as an example, such a device has a rotor mounted on a rotatable shaft, which cooperates with a coil-wound stator to provide two sinusoidal voltage read-outs, the voltage magnitude relationship and phase relationship of which indicate the instantaneous angular position of the shaft over a range from 0 to 360 degrees of rotation. Coil-wound rotors (see e.g. Logue U.S. Pat. No. 5,404,101 and Chass U.S. Pat. No. 4,445,103) have been used in such devices, but they are difficult and expensive to manufacture, and often unreliable in use because the coils may develop electrical faults.
To overcome these problems, the art has developed a number of angular position resolvers with solid rotors, thus entirely eliminating the troublesome rotor windings. See Toida U.S. Pat. No. 4,255,682; Wyss U.S. Pat. No. 6,020,737; Huard U.S. Pat. No. 5,763,976; and Ishizaki U.S. Pat. No. 5,446,966. See also Carlen U.S. Pat. No. 5,160,886, and the prior art cited therein, for solid rotors which incorporate permanent magnets instead of windings. While these rotors achieve a degree of electrical simplification, a glance at the above-cited patents shows that they come in a variety of complex mechanical configurations, which can be costly to manufacture.
Accordingly, it is the principal object of this invention to provide a solid core rotor for a rotary electrical device which is simpler in its mechanical configuration and therefore more reliable in operation as well as less expensive to manufacture.
The invention contemplates a rotary electrical device which employs a plurality of stator coils and a coil-less (i.e. solid) rotor within the stator coils comprising a ferromagnetic core having a substantially circular cylindrical configuration. The cylindrical configuration has on its surface a notch extending substantially helically thereabout for a selected circumferential distance. The notch enables the otherwise cylindrical configuration to induce respective voltages in the stator coils, the voltage magnitude relationship and phase relationship of which indicate the angular position of the rotor.
In a preferred embodiment, the axial length of the notch is equal to the axial length of the electromagnetic stator core, and the circumferential width of the notch from edge to edge is substantially 180 degrees. In some embodiments the circumferential extent of each individual edge of the notch over the axial length of the cylindrical configuration is 180 degrees, but it may also be less than that. The core is preferably formed of a stack of individual metal circular discs in facing relationship lying substantially perpendicular to the axis of the cylindrical configuration to form a series of eddy-current-blocking laminations. Each disc preferably has a semicircular gap formed at its outer periphery, and the notch is formed by skewing the semicircular laminations relative to each other at a rotational angle calculated to distribute these gaps helically over the entire core length. Alternatively, the notch could be formed by machining away a helical area of the surface of the cylindrical body.
All of the described rotor configurations are mechanically simpler and easier to fabricate than any previously known solid core rotor, and therefore are more economical, while at the same time enjoying the same electrical advantages as other solid core rotors.